In an article published in Airport Noise Report (www.airportnoisereport.com) in 2004, inventors Tom Breen and Alex Smith discuss how airport noise office needs are driven by technology and innovation in the market. The article comments on upcoming years in the airport noise monitoring business and identifies a number of positive trends in the industry. The following paragraphs are an extract from that article.
“The aviation industry is rapidly progressing towards the next generation of noise and operations monitoring systems (NOMS) as early adopters of the technology are gearing up for replacement of their legacy systems. Today's NOMS users are more sophisticated and are demanding high-tech solutions to their problems. The industry has responded and we are starting to see more innovation in the marketplace with the release of new systems and services and an increase in noise and operations monitoring patents and intellectual property.
Once the domain of expensive UNIX workstations, the NOMS market is now entirely focused on the personal computer, integration with desktop office software, and corporate networks. It is no longer satisfactory for isolated noise offices to produce weekly noise level reports on paper, plot low resolution flight tracks on a crude base map three days later, and hand type noise complaints into a database from a telephone answering machine. The next generation NOMS user is demanding real-time high-fidelity aircraft tracking and identification systems, calibrated base maps and geographic information systems, and Internet-based complaint data entry systems that feed more data than ever before into the NOMS while requiring less time from office staff.
These next generation systems are able process and provide significantly more data at a lower cost than previous systems. The Internet has revolutionized the way Americans get information and this revolution has not been lost on the next generation NOMS users who expect the Internet to be an integral part of their next NOMS. Features such as automated complaint entry systems based on Internet technology and Web-based noise office information portals are two new product trends being described in technical specifications being written today.
Another important development is the trend towards increasing data fidelity and availability in real time. The synthesis of new noise monitoring technology, improved aircraft tracking techniques, and the incorporation of other important data sources such as Digital Automated Terminal Information System (D-ATIS), will provide noise offices with more accurate information more quickly than previously thought possible.
Rannoch (Rannoch Corporation, Alexandria, Va., the assignee of the present application) has recently developed a unique capability to converge D-ATIS and other operations data with NOMS data. The D-ATIS data contains information about current weather (METAR), runways in use, field conditions, and advisories (NOTAMs), allowing AirScene™ to achieve the next dimension of awareness in terms of the airport operating conditions and flight conditions each flight experienced. Answers to questions that arise about whether airfield conditions explain why an aircraft did not follow a particular procedure are now easily and automatically explained by a report produced using Rannoch's AirScene™ NOMS.
Another interesting enhancement to the AirScene™ product line that is likely to increase data fidelity is (Rannoch's) new fully-integrated digital voice recorder. The AirScene™ voice recorder is fully integrated into the AirScene™ system. The user simply clicks the flight track of interest, and the AirScene™ digital recorder immediately plays back the ATC recordings made during that event. This automatic correlation of the digital voice recordings with the flight tracks significantly reduces the time and effort required to conduct this type of investigation.
The NOMS market is demanding innovative technological solutions and Rannoch is responding. (Rannoch) has recently joined the prestigious FAA Center of Excellence Aircraft Noise and Aviation Emissions Mitigation, created to identify solutions for existing and anticipated aircraft noise and emissions-related problems. Rannoch has also been awarded a five-year contract from the DOT's Volpe Center in Cambridge, Mass. This contract will be used to fund projects including new systems for improving aircraft tracking, surveillance, communications, air traffic management, and new technologies for airport environmental monitoring systems. These important research contracts ensure that Rannoch's internal product development is in lock step with current and future industry needs.
The fusion of automated data streams into the next generation noise and operations monitoring systems allows a level of understanding and awareness not possible a few years ago. Noise office staff members, who used to wait days for restricted-use flight tracks from the FAA, can now access high fidelity tracking information in real-time using technologies, which just a few years ago, were restricted to the military and air traffic control industry. Given the current rate of advancement and innovation we are seeing the noise and operations monitoring business, the presence of new aggressive vendors, and resurgence of the American aviation industry, the rate at which the NOMS business is changing is likely to continue accelerating over the next few years.”
The above excerpt from the Airport Noise Report article outlines some of the innovations set forth in the parent applications of the present patent application, in particular, U.S. Patent Provisional Application Ser. No. 60/440,618 filed on Jan. 17, 2003, and corresponding U.S. patent application Ser. No. 10/751,115, filed on Jan. 5, 2004, entitled “Method and Apparatus to Correlate Aircraft Flight Tracks and Events with Relevant Airport Operations Information” (Alexander E. Smith et al.), both of which are incorporated herein by reference. These parent patent applications describe how airport operations and noise monitoring may be automated using multilateration and data fusion techniques. The following paragraphs describe the background of the application of Multilateration into the Noise Industry.
Multilateration has become extremely popular for aircraft tracking in the past several years. The majority of all U.S. Noise and Operations Monitoring (NOMS) contracts in recent years use multilateration as the surveillance source. Multilateration offers tracking capabilities not available from any other techniques or systems, and is particularly useful for tracking aircraft at low flight levels and on surface areas. The following review of different multilateration systems is based on publicly available information, which is believed to be correct, but readers are advised to make their own assessment. Most of the technical information provided herein is supplied from the various vendor websites (e.g., sensis.com, era.cz, and roke.co.uk, all three of which are incorporated herein by reference) and various publicly available sources including a November 2004 report NLR-CR-2004-472, entitled Wide Area Multilateration, Report on EATMP TRS 131/04, Version 1.0, by W. H. L. Neven (NLR), T. J. Quilter (RMR), R. Weedon (RMR), and R. A. Hogendoorn (HITT), also incorporated herein by reference.
Because of the significant investment in science and engineering required to successfully commercialize and produce multilateration products, there are only three or four companies in the world that produce multilateration systems. Additionally, one or two other large air traffic control systems providers claim to be testing prototype systems or to have multilateration systems in development. For example, Siemens Roke Manor has deployed systems used for height monitoring and has stated on their website other potential applications including wide area tracking.
Companies that have actually fielded a wide area multilateration system include Sensis Corporation, ERA, and Rannoch Corporation. Sensis is a U.S. company whose clients are mainly FAA and other aviation authorities. ERA is a Czech Republic company and has several European aviation authority clients. Rannoch (assignee of the present application) is a U.S. company whose clients include FAA, NASA, and several airport authorities. Each company uses the same general concept of time difference of arrival (TDOA) measurement for multilateration. However, the methods and system architectures used by each company are very different. Each company uses remote receiver stations and a central processing system or central server. One of the key requirements for TDOA measurement is accurate time-stamping of received aircraft transponder signals. The accuracy of the time-stamping is essentially the synchronization of the system and it must be performed to within a few nanoseconds (a few billionths of a second) in order to achieve accurate tracking results.
There are three different methods in use currently to perform synchronization. Sensis Corporation uses a reference transponder technique. This approach places a fixed transmitter or set of transmitters around the airport. The transmitters emit a transponder signal, just like aircraft, but from a fixed location. The system then uses these special transponder signals as a time reference (hence the term reference transponder) and then all other received transponder signals are timed relative to the reference.
The technique works well but has two main disadvantages. The first is that the system generates it own transmissions on the 1090 MHz radar frequency and the transmitters need line-of-sight to the receiver stations. In the U.S., the FAA will not allow this approach to be used for anything other than air traffic control (ATC) or Federal Government programs, as it uses some of the available capacity of FAA's radar frequency spectrum. Antennas used by Sensis for this technique, are illustrated in FIG. 1. These antennas are rather large and bulky, and as line-of-sight antennas, may need to be properly oriented. Approximately 35 airports in the U.S. are slated to receive a Sensis ASDE-X multilateration system sometime over the next 10 years.
A second approach is the central timing technique as used by ERA. This approach relies on the central processor to perform all of the timing from a single accurate clock source. Receivers placed around the airport do not perform time-stamping, they merely receive the aircraft's transponder signal, up-convert the frequency of the signal, and transmit it to the central server. There is no time-stamping or digitizing of the signal at the receivers, they merely convert and re-transmit the received transponder signal. Since there is no digitizing or processing, there is a known fixed time delay in the conversion and re-transmission process. All of the time-stamping and digitizing can then be performed at the central server using one clock source.
This second technique has significant disadvantages. A high-bandwidth, high power microwave links are needed between each receiver and the central station, as shown in FIGS. 2A and 2B. FIG. 2A shows the separate high power antennas used by the airport central station, one for each receiver. FIG. 2B shows the high power transmitter used for each receiving station. As can be clearly seen in the illustrations, these antennas are even larger and bulkier than those of FIG. 1. In addition, as line-of-sight antennas, they require careful orientation. Such antennas are fairly expensive as well. While this second technique has been approved at some airports in Eastern and Western Europe, the FAA has not approved it for use in the United States, nor is it anticipated that the FAA will approve it in the future, due to concerns with using additional radio frequency (RF) signals within the boundaries of an airport, which may cause interference.
The manufacturer's recommended datalink frequency range is in the 10-30 GHz bands, the recommended minimum bandwidth is 28 MHz, and the datalink power ranges from 10 s to 100 s of Watts. The FAA is traditionally one of the strictest aviation authorities in terms of granting approval for radio frequency transmissions at airports. If a system is proposed for other than air traffic control applications and requires transmissions outside of approved commercial frequency bands (such as the digital WiFi 802.11 standards) it has not traditionally received approval in the United States.
A third technique is the satellite timing technique as used by Rannoch Corporation, assignee of the present application. This third technique uses satellite timing at each receiver to time-stamp received transponder signals. There are several satellite systems available including the U.S. Global Positioning System (GPS). The Rannoch AirScene™ system uses a patented (U.S. Pat. No. 6,049,304, incorporated herein by reference) technique for satellite synchronization, which is accurate to a few nanoseconds. In addition, the system offers advantages in equipment installation, as no line-of-sight is needed between receivers and the central station. Most importantly, there is no need to transmit any signals whatsoever, as data from receivers can be sent to a central station via non-radio techniques (e.g., hardwire, internet, local network, or the like). FIG. 3 illustrates one of Rannoch's receiver units combined with weather instrumentation into a compact installation package. From left to the right the items are: GPS, rainfall device, pressure device, wind speed and direction unit, and radar receiver unit. Note there are no transmitters in this package, and thus no additional RF signals are generated. Thus, FAA approval may not be required for such an installation. As illustrated in FIG. 3, the antenna installation of this third technique is much more compact, less expensive, and less obtrusive than the installations of the first two techniques as illustrated by FIGS. 1, 2A, and 2B.
A fourth technique is a height monitoring multilateration used by Siemens Roke Manor Research. Siemens was one of the pioneers of multilateration to determine aircraft height (i.e., altitude) for the reduced vertical separation program. Working with various governments and industry partners, Siemens deployed a handful of these sophisticated height measurement units. The company is believed to be embarking on an ambitious development program to apply this technology to commercial wide-area tracking.
The original height measuring devices used components and subsystems from many different suppliers, which made the overall systems very expensive. The systems were priced in the region of $10M USD each. As of October 2005, there are no known mature operational Siemens systems used for airport tracking applications such as NOMS. In mid 2005, in an independent assessment of the operational maturity of multilateration technologies, the German government (DFS) found only four companies to be qualified (Sensis, Rannoch, ERA, and Thales). Other systems, including the Siemens Roke Manor system, were not qualified by DFS as operationally mature at that time for airport tracking applications.
The different multilateration techniques are summarized in Table 1. Table 1 includes a column titled “active system.” An active system is defined as one that needs to interrogate each aircraft to elicit a transponder reply. Of the four, only the Sensis system needs to interrogate aircraft, which is fundamental to the design of that system. The ERA and Rannoch systems do not need to generate interrogation signals as they both are designed to handle most aircraft transponder replies to a variety of other sources, such as ground radar or aircraft collision avoidance devices. Therefore, both the ERA and Rannoch systems can be classified as “passive” within the traditional definition of “active” and “passive.”
However, this classification does not mean that all passive systems do not use radio frequency transmissions for some functions; it means only that the passive system does not interrogate aircraft transponders. As noted previously, the ERA “passive” system needs a high bandwidth microwave link (as illustrated in FIGS. 2A and 2B) and therefore must transmit high power signals constantly in airport environments, which is strictly prohibited at U.S. airports. The “passive” Rannoch system, on the other hand, does not transmit on any frequency for any purpose, and is used by the U.S. Federal Government for several monitoring projects and is authorized for non-air traffic control purposes, such as noise monitoring, at U.S. airports. Thus, as illustrated in Table 1, of the four multilateration systems available, only one, the Rannoch system, is truly passive, does not require generation of radio transmissions, and has been successfully implemented for airport noise and operations monitoring.
FIG. 4 illustrates an example of a real-time Rannoch AirScene™ display (in this example, from Louisville) and illustrates the ability of the system to provide data parameters from multiple AirScene™ sources in real time. In the example of FIG. 4, data blocks selected by the user for display include Mode A code (squawk), flight number (call sign), tail number, aircraft type, Mode C altitude, flight level, and origin and destination. AirScene™ can supply or use any of these data sources. The example shown is unique to AirScene™, as no other NFTMS can display all of the information as shown in real time. Other vendor approaches require extensive post-processing to match up the tail number with all of the other data.
FIG. 5 illustrates the same system when the operator queries a particular aircraft by highlighting it (UPS 6058 on the top right). All of the associated identification data is shown in the hyper-box on the right. When using AirScene™ multilateration tracking, runway utilization is very accurate, as the system will usually track the departure accelerating along the surface through rotation and departure. In the two examples of FIGS. 4 and 5, the user has selected all of the colors, icons, and GIS layers, including the 5 NM range rings shown.
As noted previously, the FAA is implementing an ASDE-X Multilateration Program in as many as 35 airports in the next 10 years in the United States. Many airport managers and operators have questions regarding the application of the ASDE-X program to commercial tracking applications. The following is an overview of the ASDE-X program and answers to frequently asked questions regarding that program.
The Airport Surface Detection Equipment-Model X (ASDE-X) program was initiated in 1999 and Sensis Corporation was selected as the vendor in the year 2000. The Senate Committee on Appropriations, in its report on FAA's fiscal year (FY) 2006 appropriations, expressed concern about the pace of ASDE-X deployment and reported that the FAA has not yet deployed systems to more than half of the planned sites due to changes in system design and additional requirements. The FAA originally planned to complete ASDE-X deployment to second-tier airports (e.g., Orlando International Airport and Milwaukee General Mitchell International Airport) by FY 2007 as a low-cost alternative to Airport Surface Detection Equipment-3 (ASDE-3) radar systems, which are deployed at larger, high-volume airports. However, the FAA now plans to complete deployment by FY 2009, resulting in a two year delay. While FAA has already procured 36 out of 38 ASDE-X systems, only three systems have been commissioned for operational use as of late 2005. FAA has invested about $250 million in ASDE-X and expects to spend a total of $505 million to complete the program. (See, e.g., www.faa.gov). A map of planned ASDE-X installations (from www.asdex.net, incorporated herein by reference) as well as upgrades to the older ASDE-3 systems is illustrated in FIG. 6.
One question airport operators have is that if the FAA plans to install ASDE-X at their airport, what additional benefits, if any, would be provided by an AirScene™ system? The answer is that airports should be aware of realistic dates to receive an ASDE-X system, based on the delays and cost overruns associated with program. Once installed, the ASDE-X will provide coverage only on the movement areas, not in the terminal area, on the ramps, aprons, or to the gates. Furthermore, the ASDE-X system is an FAA system and airport access to the data is not guaranteed on an unrestricted or even on a restricted basis.
Thus, a number of ASDE-X airports have contracted for and are currently using an AirScene™ tracking system. These airports include T. F. Green State Airport, Providence, R.I., San Antonio International Airport, TX, and Raleigh Durham International Airport, NC. Several more ASDE-X airports are currently in contract negotiations and discussions for an AirScene™ system.
Another question airport operators ask is if their airport is receiving an ASDE-X system for the runways and taxiways (movement areas) would it just be a small incremental cost to add coverage at the gates, ramps, and aprons? While it would seem logical that the costs would be incremental, based on experiences at several airports, the cost of adding to a planned ASDE-X installation can be significantly higher than the installation of a complete stand-alone AirScene™ airport management system. Furthermore, adding onto an ASDE-X installation ties the program schedule to the FAA's schedule and involves the FAA directly in the airport's program. As a stand-alone system, the Rannoch AirScene™ does not require regulation, intervention, monitoring or interaction with the FAA or Air Traffic Control systems. Thus, an airport manager or operator can implement and operate the Rannoch AirScene™ system without having to obtain permission from the FAA and without government interference.
Another question is whether the ASDE-X system affects the performance of the AirScene™ system and/or whether the AirScene™ system affects the ASDE-X system. As noted above, the Rannoch AirScene™ system is a truly passive system. Thus, there are no detrimental effects to either system when they are both operational at the same airport. On the contrary, the presence of an ASDE-X system generates more transponder replies for the AirScene™ system to detect and build aircraft tracks. Since AirScene™ is a passive system; it causes no interference to the ASDE-X system whatsoever.
Another concern of airport operators is that is seems that there is a lot of work involved in finding sensor sites for ASDE-X sensors, and arranging telecommunications, particularly when some of the sites are located off airfield. AirScene™, however, uses small compact sensors and antenna (See, e.g., FIG. 3), which can be located virtually anywhere (on-site or off-site), and the communications are flexible, ranging from telephone lines, to TCP/IP, or other industry standard forms of communication. Off-airport sites pose a significant challenge for ASDE-X due to problems with eminent domain, lease arrangements, and physical siting constraints due to the need for all ASDE-X sensors to have line-of-sight to the airport.
In contrast, AirScene™ sensors do not need line-of-sight to the airport and are so small that they can be mounted atop shared wireless communication towers. Through a contract with cell providers, AirScene™ has access to over 20,000 towers across the country. Therefore, there are few, if any issues of eminent domain, leasing, or siting with an AirScene™ system. Table 2 illustrates a comparison summary between ASDE-X and the AirScene™ system. As illustrated in Table 2, only the AirScene™ system presently provides a practical system for airport management.
From the foregoing description, it is quite clear that the only practical system for airport NOMS presently available is the Rannoch AirScene™ system. However, airports are becoming increasingly complex as a result of increased security concerns, increased traffic flow, cost reduction pressures, and the like. As a result, it is desirable to expand the capabilities and further enhance the AirScene™ system to provide additional features, which are of use to airport managers and operators in both the day to day operations of an airport, as well as in future planning and management. The present invention incorporates these improvements to the Rannoch AirScene™ NOMS.